In an Internet protocol/wavelength division multiplexing (IP/WDM) network that is formed by combining an IP network and an optical network (WDM network) based on the WDM technology, the IP network is overlaid on the WDM network. The WDM network and IP network are referred to as a WDM layer (Or an optical layer) and an IP layer, respectively. The WDM layer, formed with an optical cross-connect (OXC), may create a logical communication channel referred to as a lightpath (or an optical path) between arbitrary two nodes. When setting a lightpath, a wavelength common to a pair of nodes coupled by the lightpath is usually used, thereby allowing a communication channel with a large capacity equivalent to the capacity of one wavelength (for example, 10 Gbps or 40 Gbps) to be logically created between the pair of nodes.
Two nodes linked by a lightpath become mutually adjacent nodes on the IP layer, and a router connected in correspondence to an intermediate OXC through which the lightpath passes is cut through, eliminating the need for a packet transfer process from the router. Power consumption per unit bit rate in a transfer process by the OXC is smaller than power consumption per unit bit rate in the transfer process by the router. Whereas granularity in the transfer process by the OXC is larger than granularity in the transfer process by the router.
In view of the above situation, a technology to achieve small power consumption by a node device on a network including lightpaths with different quality levels is proposed, in which the node device has a plurality of error correcting decoders and does not carry out subsequent correction decoding when an error is corrected before a maximum number of repetitions in iterative decoding is reached (for example, see Japanese Laid-open Patent Publication No. 2010-166378). In another technology in which a reward for successful lightpath setting and a cost for failed lightpath setting are preset in a table for each service class, whether to accept a lightpath setting request is determined with reference to the table so as to achieve effective usage of lightpaths and differentiate service classes (for example, see Japanese Laid-open Patent Publication No. 2010-263442).
In another technology to preventing optical regenerators from generating signal errors, lightpath settings are monitored by a monitoring control unit and whether to allow transmission through a new lightpath is determined from topology information, path information, and other information that are held by the monitoring control unit, so that incorrect settings are prevented (for example, see Japanese Laid-open Patent Publication No. 2010-62647). In a method of searching for an optimum lightpath on a mesh optical WDM network, a new lightpath topology is initialized and two nodes are selected by using random numbers, after which whether a lightpath is allowed to be set between the two nodes is determined, whether lightpaths have been assigned to all transmission and reception interfaces is determined, and whether the new lightpath topology forms a connected graph is determined. These processes enable a search for an optimum lightpath topology without searching for lightpath topologies of all patterns (for example, see Japanese Laid-open Patent Publication No. 2006-253786).
A method of selecting a lightpath and calculating a path is also proposed that creates an auxiliary graph that includes a virtual topology layer and a physical layer and uses the power consumption of routers and the power consumption of optical fibers as the weights of edges so as to obtain a path having a least power consumption, and an effect of reducing power consumption on an IP/WDM network is indicated (for example, see M. Xia, M. Tornatore, Y. Zhang, P. Chowdhury, C. U. Martel, and B. Mukherjee, “Green Provisioning for Optical WDM Networks”, IEEE Journal of Selected Topics in Quantum Electronics, vol. 17, no. 2, pp. 437-445, March 2011).